1. Field of the Invention
The present invention relates to colored molded articles.
2. Description of Related Art
Conventionally, a long molded article, such as a side molding for an automobile or the like, has been produced using colored synthetic resins prepared by blending a coloring pigment with the synthetic resin (hereinafter referred to as "colored resin").
As FIG. 11 shows, a colored side molding 7 for an automobile using conventional colored resins is composed of a long main body 71 and a thin plate 72 integrally formed therewith along a side edge of the main body. The thin plate 72 has a thickness less than that of the main body 71 so that a decorative batten 75 is pasted on an upper surface 721 of the thin plate 72. Two-sided tape 76 is used for adhering the batten 75 to the side molding 7.
The colored resin for making the aforementioned conventional side molding 7 contains a glitter material as the coloring pigment containing aluminum powder or the like. The side molding 7 produced by injection molding such a coloring pigment exhibits vivid metallic color over an entire surface thereof requiring no coating, resulting in a highly added value of the desired appearance.
However, the above-obtained side molding 7 using conventional colored resins has the following problems.
As FIG. 12 shows, several undesirable lines 79 are left on the surface of the side molding 7 along the flow direction of the resin around the boundary between the main body 71 and the thin plate 72. Such lines are typically referred to as orientation irregularities, flow traces, or the like.
The cause of the aforementioned orientation irregularities is hereinafter explained. As FIG. 13 shows, within a mold 78 for injection molding, the resin flowing through the mold space for forming the main body 71 (thicker than the thin plate 72) at a center of the mold 78 moves faster than that flowing through the mold space for forming the thin plate 72 near the edge of the mold 78. Therefore, the mold space for forming the thin plate 72 is filled with the colored resin flowing from the main body 71. At this time, a large degree of turbulence may occur in the flow of the colored resin around the boundary between the main body 71 and the thin plate 72. As a result, such turbulence in the resin flow is now believed to cause unevenness on the resultant product surface, thus degrading its appearance.
This type of phenomenon similarly occurs when using a standard colorant as the coloring pigment. The phenomenon is further likely to occur when using glitter materials exhibiting glitter as the coloring pigment, particularly, having a needle-like shape or a flat shape. The orientation irregularity tends to occur easily as the particle size of the coloring pigment becomes smaller and a content thereof becomes larger.
Conventionally, painting has been only a way to provide the beautiful and solid appearance such as deep metallic luster, pearl tone or the like to the surface of the molded resin produced from a thermoplastic resin or the like.
However, the painting method requires complicated processes, such as degreasing and flushing the surface of the molded product, prime coating, intercoating, topcoating, dust removal, drying, baking as well as expensive facilities and paint.
Accompanied with the prolonged cycle time for the above processes, the production cost is further increased.
In order to produce the molded resin exhibiting metallic luster and pearl-like tone at a lower cost, the colored resin prepared by adding the glitter material as an essential additive has been used for molding. The above colored resin is obtained by mixing the glitter material such as metallic fragment (scaly aluminum powder) or mica directly with the resin together with the colorant for producing the metallic luster and the pearl-like tone. The molded product using the aforementioned colored resin is called the molded colored article.
Referring to FIGS. 14 to 17, on an upper surface (design surface) 98 of a molded colored article with a boss integrally molded therewith, a flow trace 95 is occasionally generated along with the flow direction of the resin (FIG. 16). FIGS. 14 and 15 show a molded colored article 90 as a long molding having a cross-shaped boss 91 integrally molded therewith on a back surface 99. The boss 91 serves to position the molded colored resin 90 in place to be fixed to the side of the automobile. A reference numeral 92 of FIG. 14 represents an adhesion tape attached to the back surface 99 of the molded colored article 90.
Referring to FIG. 16, the flow trace 95 is occasionally generated downstream of the boss 91 along the resin flow direction "N" of the colored resin flowing from a gate K to the gate D opposite thereto during molding.
A similar phenomenon also occurs in case of mounting a column-shaped boss 97 as shown in FIG. 17. The molded colored article having the boss is prepared by injection molding the above-described colored resin into a cavity of the mold and then integrally molding the boss and a main body of the molded colored article simultaneously.
A flow trace 95 is likewise generated on a molded colored article 8 of a sandwich construction having an outer skin layer formed of the colored resin and a core layer formed by supplying hard material to the inside of the skin layer as shown in FIG. 18.
More specifically, the flow trace 95 is generated around upper surface of a curve part 80 of the molded colored article 8. One end of the molded colored article 8 is bent at a gate D opposite to the gate K from where the resin is supplied for molding to form an L-like shape as a bent end 84.
The molded colored article 8 of a sandwich construction is molded by injecting the colored resin 81 for a skin layer into a cavity 871 of a mold 87 and then injecting resin for the core layer 82 into the inside of the skin layer. A tab 88 is provided at an end of the mold space for forming the bent end 84 so as to accommodate excessive resin 880 to overflow thereinto as shown in FIG. 19.
The flow trace 95 generated on the upper surface of the respective molded colored articles 9 and 8 shown in FIGS. 16 and 17 is called as "uneven metallic luster", which degrades design quality of the resultant molded colored article. A sink mark is further generated on the part where the aforementioned flow trace is generated.
Various kinds of examinations have been conducted with respect to injection pressure to the colored resin, control of the resin flow rate or the like in order to prevent generation of the above-described flow trace and the sink mark. However, owing to difficulty in establishing the molding conditions, satisfactory results have not been realized yet.